Magnetic resonance scanners are imaging devices that, for mapping an examination object, align nuclear spins of the examination object with a strong external magnetic field and excite the nuclear spins to precession around this alignment via a magnetic alternating field. The precession or return of the spins from this excited state into a state with lower energy in turn generates in response a magnetic alternating field, also known as a magnetic resonance signal, which is received by antennas.
By magnetic gradient fields, spatial encoding is impressed on the signals and this subsequently enables allocation of the received signal to a volume element. The received signal is then evaluated and a three-dimensional imaging representation of the examination object is supplied.
Magnetic alternating fields having a frequency corresponding to the Larmor frequency at the respective static magnetic field strength and very high field strengths or outputs are required for excitation of the precession of the spins. Antennas, frequently called local coils, arranged directly on patient are used to improve to improve the signal-to-noise ratio of the magnetic resonance signal received by the antennas. Local coils may have a plurality of individual antennas, which may also be called coil elements. The coil elements may be embodied as coil loops.
However, individual patients differ considerably in their physiognomy with the result that, with a rigid local coil, either an optimum signal is obtained for a few patients only or it is necessary to keep available many local coils with different dimensions.
An aim in imaging is to bring the coils as close as possible to the patient, (e.g., to the body region to be examined), in order in this way to achieve the best possible signal-to-noise ratio. To this end, conventionally a differentiation is made between rigid coil types configured to a respective body region and flexible coil types.
Rigid coils may be used for head examinations and may be configured to the special anatomy of the head. Head coils are known, for example, from the publications U.S. Pat. No. 8,244,328 B2; U.S. Pat. No. 9,138,164 B2; U.S. Pat. No. 7,826,887 B2; U.S. Patent Application Publication No. 2015/0057527 A1; and U.S. Patent Application Publication No. 2015/0057528 A1. However, image quality may be degraded in the case of patients with small heads because the antenna structures are not optimally close to the anatomy.
Flexible coil structures may compensate lack of adaptation, but a conventional problem is that such arrangements also only enable three-dimensional conversions to a restricted extent. This results in bulging and the protrusion of sub-regions of the coil arrangement. For example, in the case of cylindrical body shapes, (e.g., knees or elbows), depending upon the diameter, there may be another overlap or a gap between two coil ends. As a result, the image quality achieved is not optimum.
German Patent Publication No. DE 10 2011 007 065 A1 discloses a knee coil, wherein the receiving part includes a rigid-flexible combination.